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Vapor-Compression Cycle (Edited from Wikipedia)

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Vapor-Compression Cycle (Edited from Wikipedia) Vapor-Compression Cycle (Edited from Wikipedia) SUMMARY Vapor-Compression Refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air-conditioning of buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems. Refrigeration may be defined as lowering the temperature of an enclosed space (like a house or refrigerator) by removing heat from that space and transferring it elsewhere. A device that performs this function may also be called an air conditioner, refrigerator, air source heat pump, geothermal heat pump or chiller (heat pump). HISTORY In 1805, the American inventor Oliver Evans described a closed vapor-compression refrigeration cycle for the production of ice by ether under vacuum. Heat would be removed from the environment by recycling vaporized refrigerant, where it would move through a compressor and condenser and would eventually revert to a liquid form in order to repeat the refrigeration process over again. In the postscript of his Steam Engineer's Guide , Evans noted that drawing a vacuum on water reduces its boiling point and cools it. He further observed that a vacuum would have the same effect upon ether, and the resulting cooling should be sufficient to produce ice. He went on to describe a piston vacuum pump apparatus to produce this effect, and also showed that a compression cylinder, or the compression stroke of the vacuum pump, should produce heat in a condenser. Thus Evans had produced the first detailed and theoretically coherent design for a vapor-compression refrigerator, identifying all the major components (expander, cooling coil, compressor and condenser) of a refrigeration cycle, leaving some to credit him as the 'grandfather of refrigeration'. Although Evans never developed a working model of his designs, and 1 there is no evidence that he ever attempted to, Evans in his later life worked and associated extensively with fellow inventor Jacob Perkins on steam engines and the potential for refrigeration. In 1834, an American expatriate to Great Britain, Jacob Perkins, built the first working vapor-compression refrigeration system in the world. It was a closed-cycle that could operate continuously, as he described in his patent. His prototype system worked although it did not succeed commercially. A similar attempt was made in 1842, by American physician, John Gorrie, who built a working prototype, but it was a commercial failure. American engineer Alexander Twining took out a British patent in 1850 for a vapor compression system that used ether. The first practical vapor compression refrigeration system was built by James Harrison, a British journalist who had emigrated to Australia. His 1856 patent was for a vapor compression system using ether, alcohol or ammonia. He built a mechanical ice-making machine in 1851 on the banks of the Barwon River at Rocky Point in Geelong, Victoria, and his first commercial ice-making machine followed in 1854. Harrison also introduced commercial vapor-compression refrigeration to breweries and meat packing houses, and by 1861, a dozen of his systems were in operation in Australia and England. The first gas-absorption refrigeration system using gaseous ammonia dissolved in water (referred to as "aqua ammonia") was developed by Ferdinand Carré of France in 1859 and patented in 1860. Carl von Linde, an engineering professor at the Technological University Munich in Germany, patented an improved method of liquefying gases in 1876. His new process made possible using gases such as ammonia, sulfur dioxide (SO2) and methyl chloride (CH3Cl) as refrigerants and they were widely used for that purpose until the late 1920s. HOW IT WORKS The vapor-compression cycle uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to be cooled. It then rejects that heat elsewhere. All such systems have four components: a compressor, a condenser, a thermal expansion valve (also called a throttle valve or metering device), and an evaporator. Circulating refrigerant enters the compressor in the thermodynamic state known as a 2 saturated vapor and is compressed to a higher pressure, which also raises the refrigerant’s temperature. The hot, compressed vapor is then in the thermodynamic state known as a superheated vapor. It is at a temperature and pressure at which it can be condensed with cooling air flowing across the condenser coil. This is where the circulating refrigerant rejects heat from the system, and the rejected heat is carried away by the air blowing across the condenser coil. The refrigerant is condensed back into a liquid because it has been “cooled” from a gas back into a liquid (similar to how water vapor condenses back into a liquid). The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. This also lowers the temperature of the liquid-vapor refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated. The cold mixture is then routed through the coil or tubes in the evaporator coil. A fan blows the warm air from the enclosed space (such as the inside of a refrigerator or your house) across the coil or tubes carrying the cold refrigerant. The refrigerant absorbs the heat in the warm air, which heats it up and causes the cold liquid refrigerant to evaporate (similar to when water is heated to boiling and evaporates). At the same time, the air is cooled and blown back into the enclosed space, which lowers the temperature of the enclosed space to the desired temperature. The evaporator coil is where the circulating refrigerant absorbs and removes heat. To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again transformed into a saturated vapor and is routed back into the compressor. 3.
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